Marine electrical speedometers

ABSTRACT

Marine speedometers having a submerged electrical generating unit electrically connected to a remotely located indicating unit. The generating unit comprises an impeller driven rotating magnetic field inducing an alternating current in a stationary winding which is connected, through a current rectifying electrical circuit, to an electrical meter forming the indicating unit.

United States Patent Kirk [4 1 Apr. 25, 1972 [541 MARINE ELECTRICAL2,103,606 12/1937 Abrahamsohn et a1 ..324/11s SPEEDOMETERS 3,287,96911/1966 Hardy'. ..73/187 3,321,969 5/1967 S encer, Jr ..73 187 [72]Inventor: William H. Kirk, i109 W. Selfridge, p Clawson, Mich. 48017FOREIGN PATENTS OR APPLICATIONS [22] Filed: June 30, 1967 854,77511/1960 Great Britain ..73/l87 357,163 3/1938 Italy ..324/70E [21]650,269. 502,516 1111954 Italy ..73/1s9 R l t d U.S. A li t Data 8 a epp ca Primary ExamineF- DOnald O. Woodie] [63] Continuati0n-in-part ofSer. No. 433,323, Feb. 17, Atrorneyl-lauke,Gilford and Patalidis 1965,abandoned.

[57] ABSTRACT [52] U.S.Cl ..73/187 1 [51] Int. Cl ..G01c 21/10 M P Qhaving a Submerged i al generat- [58] Field 0 Search 73/181 185 mg unitelectrically connected to a remotely located 1ndicating unit. Thegenerating unit comprises an impeller driven rotating magnetic fieldinducing an alternating current in a References Cited stationary windingwhich is connected, through a current rectifying electrical circuit, toan electrical meter forming the UNITED STATES PATENTS indicating unit-2,004,724 6/1935 Herzog.; ..324/1l5 17 Claims, 16 Drawing FiguresPATENTEDAPR 2 5 m2 SHEET 1 [IF 3 FIG.- 2

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I46 e 4e sow INVENTOR. WILLIAM H. KIRK ATTORNEYS PATENTEDAPR 25 I972 3,6 ST. 924

SHLEI E OF 3 WILLIAM H. KIRK BY M, flan 4% "M ATTORNE Y$ CROSS REFERENCETO RELATED APPLICATION The. present application is acontinuation-in-part of now Heretof ore several different typesofsystems for sensing and indicating. the speed of marine craft andthelike have been provided. These systems-have generally taken one of threedifferent basic forms: The first of these general types utilizes animpeller to sense the speed ofthe craft and a flexible shaft connectedto the impeller to actuate a remotely positioned indicating means. Suchsystems are not very accurate especially at low speeds because of thefrictional resistance to the rotating shaft.

The second general type of marine speed indicating means presently inusecomprises the utilization ofa Pitot tube for sensing the speed ofthecraft and some other type of means actuated in response to the changesin pressures produced within thePitottube to indicate the speed. Becausethe pressure changes in such'tubcs vary at a rate corresponding to thesquare of the speed, the indicating means must include some type ofcompensating'device or a non-linear scale. For this reason such systemshave been quite expensive to manufacture and have been quite inaccurateespecially at low speeds.

The third general type of marine speed indicating systems comprises anelectrical circuit including a magnetized impeller for-sensing the speedof the craft and a separate circuit for amplifying the sensedfluctuations in current to actuate a meter indicating the speed of thecraft .'Such a system is much more accurate than the heretoforementioned systems but has the disadvantage that a separate power sourceis required for the amplifying circuit. The seperate power generallycomprises a set of dry cell batteries and it is of course necessary toperiodically replace the batteries to keep the system in operatingcondition. This is an inconvenience and often results in the systembeing inoperative at a time when it is needed and when his not possibleorconvenient to replace the depleted batte ries.

The present invention provides a system having some analogy with thelast mentioned system in that it is electrically actuated. Unlikethelast mentioned system, however, the system of the present inventionutilizes an impeller to drive a small electrical generator. The impelleris responsive to the speed of the craft and the generator produces anelectrical current which varies substantially proportionally to thespeed of the craft. The current produced by the generator is transmittedby way of appropriate current rectifying means to a meter which measuresthe amount of current produced by the generator andindicatesthisamountinterms of the speed of the craft. Since a separate amplifying circuit isnot necessary, external power source and complicated electrical circuitsare 7 eliminated. This eliminates the possibility of the system beingnon-operable because of depleted batteries.

The prior art known to applicant further includes Gualandi Italian Pat.No. 502,516 and Hardy U.S. Pat. No. 3,287.969. Gualandi provides for animpeller driven hub rotatinga shaft projecting within ahousing. Theshaft is supported in the housing by means of ball bearings and supportsa rotating magnet forming an axial gapwitha coil into which analternatingcurrent is induced as a result of the rotation of themagnet.Such an arrangement is fragile and vulnerable as it must of necessityinclude sealing means preventing the introduction of water into thehousing, andit includes no provision for adjusting the magnetic gap andrequires precise alignmentbetween the stationary parts, including. thepole pieces of'thecoil, and the rotating. parts, including. the rotatingmagnet mounted on the shaft. Hardy provides for an impeller driven hubcarrying a pair of U-shaped magnets forming an axial gap with the polepieces of the coil core fixedly disposedin a housing. The coil core ismade of laminated material and is U-shaped with the coil wound aroundthe bridge portion connectingthe two legs of the U-shaped core. Theshaft on which the impeller driven hub is rotatably mounted projectsfrom the housing and the hub is held in position by a washer and nutassembly such that there are two separate pair of surfaces in frictionalengagement with one another with the resulting increase in friction andsubstantial possibility of dirt being introduced between rotatingsurfaces and resulting in preventing the hub from rotating freely.

The speedometers of the present invention provide for simple and ruggedconstruction, for small size units having rotating parts endowed withsubstantially small inertia and, in addition, the speedometers of thepresent invention are constructed in a unique manner to produce onlynegligible friction losses so that even low speeds are indicated with arelatively high degree of accuracy. This is accomplished not only by theparticular electrical actuating means employed but by an improvedconstruction for the impeller and generator. The magnets are made ofmaterial such as ferrites and the like, and carried within a rotatinghub which carries on its exterior surface the blades which form theimpeller. The encapsulated and sealed electromagnetic coil is carried ina housing in a fixed position axially spaced from the magnets. Fixed magnetic core members direct the flux produced by the mating magnets to theelectromagnetic coil. By utilizing the hub to carry both the impellerblades and the magnets, it is assured that the magnets rotate at exactlythe same speed as the impeller and frictional losses due to rotatingseals are eliminated. By fixing the coil and rotating the magnetsrelative to and axially spaced from the coil, the necessary electricalconnections can be made with the coil without requiring expensive andfriction-producing slip type connections. The particular arrangement andconstruction of the impeller and generator portions of the presentsystem, moreover, permit these portions to be carried in a smallstreamlined compact housing so that the system itself does not interferewith the speed of the craft. In addition the structure of the inventionpermits adjustment of the axial magnetic gap for calibration purposesand provides means for compensating axial play in the rotating spindle.

A particular arrangement of the electrical system of the presentinvention permits ready adjustment for varying the effect that changesin the current producedwill have on the indicating pointer of thesensing meter. This can be accomplished by providing means within theelectrical circuit for selectively varying the effective resistancebetween the generator and the meter. To take advantage of this, thepresent invention provides a mechanical means actuated when theresistance in the circuit is varied to provide a new set of indicia onthe indicator selected range of speed being indicated.

SUMMARY OF THE INVENTION It is an object then of the present inventionto improve marine speedometers by providing means generating anelectrical current in accordance with the speed of the craft and meansindicating the value of the current generated to thereby visiblyindicate the speed of the craft.

It is another object of the present invention to improve the accuracyand reliability of marine speed indicating means and the like byproviding a rotatably mounted hub member carrying magnets and providedwith means to produce rotation of the hub member and the magnets inaccordance with the speed of the marine craft, an electromagnetic coilcarried in a fixed position axially spaced from the magnets, magneticmembers directing the flux produced by the magnets to theelectromagnetic coil, and meter means connected with the coil andindicating the current generated therein in terms of the speed of thecraft.

plate corresponding to the particular ing means to indicate the currentgenerated in terms of the speed of the craft, means for providing anexpanded speed indicating scale for low speed range or alternately forselectively varying the resistance between the generating means and themetering means to thereby vary the effect changes in current will haveon the metering means and to provide a means for varying the range ofspeed indicated and means actuated by the resistance varying means tovary the indicia on the indicator plate of the metering means inaccordance with the particular range of speed being indicated by themetering means.

Still further objects and advantages will readily occur to one skilledin the art to which the invention pertains upon reference to thefollowing drawings in which like reference characters refer to likeparts throughout the several view and in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal sectionalview of the generator portion of a first preferred embodiment of aspeedometer of the present invention; I

FIG. 2 is a transverse sectional view taken substantially at line 2-2ofFIG. 1;

F IG. 3 is a transverse sectional view taken substantially at line 3-3of FIG. 1;

FIG. 4 is a front elevational view of a first preferred embodiment ofthe indicating means of the speedometer of the present invention;

FIG. 5 is a cross sectional view taken substantially on line 5-5 of FIG.4 with some portions illustrated in elevation and other portions removedfor purposes of clarity;

FIG. 6 is a front elevational view of a portion of the structure shownin FIG. 4;

FIG. 7 is a fragmentary cross sectional view taken substantially on line7-7 of FIG. 5 and enlarged somewhat for purposes of clarity;

FIG. 8 is aschematic illustration of a preferred electrical circuit forthe system of the present invention for use in combination with thespeed indicating unit of FIGS. 4-7;

FIG. 9 is a longitudinal sectional view of a modification of thegenerator portion of the speedometer of the present invention;

FIG. 10 is a transverse sectional view taken substantially at line 10-10of FIG. 9;

FIG. I1 is a schematic perspective view of the coil magnetic core andpole pieces of the speedometer generator portion of FIG. 9;

FIG. l2 is a transverse sectional view taken along substantially line12-12 of FIG. 9, with the impeller blades omitted;

FIG. 13 is a view similar to FIG. 12, but showing a modification of thehub magnet arrangement;

FIG. 14 is a schematic perspective view of the magnet arrangement ofFIG. 13;

FIG. 15 is a schematic modified electrical circuit for the presentinvention; and

FIG. 16 is a front elevational view of a modified indicating means forthe speedometer of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Now referring to the drawingsfor a more detailed description of the present invention, a firstpreferred embodiment of speed sensing and indicating system isillustrated as comprising a speed sensing means generally indicated at10 in FIG. 1 and a speed indicating means generally indicated at 12 inFIGS. 4-5. The speed sensing means 10 is preferably connected with theindicating means 12 by the electrical circuit illustrateddiagrammatically in FIG. 8.

As can best be seen in FIGS. 1-3, the speed sensing means 10 preferablycomprises a cylindrical housing member 14 provided at one end with areduced diameter axially annular flange portion 16. A hollow mountingstructure 18 is provided with an internal annular recessed portion 20adapted to receive the flange portion 16 of the housing member 14. A

plurality of annularly spaced set screws 22 carried by the mountingstructure 18 engage the flange portion 16 to secure the housing member14 to the mounting structure 18. An 0- ring seal 24 disposedintermediate the ends of the flange portion 16 and the recessed portion20 prevents fluid leakage therebetween.

The mounting structure 18 preferably comprises an upstanding portion 26terminating in an upper face 28 which closes the mounting structure 18.A tubular member 30 communicates with the interior of the mountingstructure 18 and is secured to the mounting structure 18 so as to extendupwardly from the face 28.

Means for mounting the speed sensing means 10 to the underside of amarine craft or the like (not shown) are carried by the tubular member30 and preferably comprise a hollow threaded tubular bolt 32 axiallyslidably receiving the tubular member 30 and having at its lower edge anenlarged flange portion 34. The bolt 32 is adapted to receive a flangednut 36. The bolt 32 is secured to the tubular member 30 by a nut 38received by the threaded upper end of the tubular member 30.

The flange portion 34 is adapted to seat against the upper face 38 ofthe mounting structure 18 and a'pin 40 may be provided if desired toinsure proper positioning of the flange portion 34 with respect to theface 28.

The central housing member 14 is preferably provided with a cavity 42registering with the interior of the mounting structure 18. Anelectromagnetic coil 44 is preferably substantially centrally positionedwithin the cavity 42 by means of an enveloping layer of rubber, plasticor similar material as indicated at 46. Rod-like magnetic core members48 of a suitable magnetic material are carried on opposite sides of thecoil 44 and extend longitudinally in appropriate cavities 49 in centralhousing member 14 from an area in registry with the cavity 42 to a pointclosely adjacent the free end of the central housing member 14. A coverplate 50 made of suitable nonmagnetic material closes the centralhousing member and forms a flat end face thereof. Radially extendingmagnetic members 52 magnetically connect the coil 44 with the coremembers 48.

A shaft 52 is fixed in the free end of the housing member 14 by havingfor example, one of its ends press fitted in an axial bore 53 andextends axially forwardly therefrom to provide the means for rotatablycarrying a hub 54. The hub 54 is rotatably mounted on the shaft by meansof a nut'member 56 received by the threaded free end of the shaft 52 anda pair of axially spaced bearing sleeves 58. The end of the hub 54adjacent the housing member 14 is provided with an axially extendingcavity 60 which provides the means for carrying a plurality ofindividual axially extending and annularly spaced magnets 62. Themagnets 62 are positioned with their poles alternately disposed flushwith flat end face 61 of hub 54 and closely adjacent the end plate 50 ofthe housing member 14 so that, as the hub' 54 is rotated, the lines ofmagnetic force produced by the magnets 62 are cut by the fixed magneticcore members 48. An enveloping layer of suitable plastic material asindicated at 63 fills the cavity 60 and encloses the magnets 62. Theouter surface of the hub 54 is provided with a plurality of tapered andhelically disposed fins 64.

The forward end of the hub 54 is provided with an internally threadedrecess 66 which provides the means for receiving a nose member 68. Thenose member 68 carries an insert 70 which is preferably constructed ofnylon or the like and which upon tightening of the nose member 68 intothe recess 66, engages the end of the shaft 52. The insert 70 permitsthe hub 54 to be moved axially slightly away from the housing member 14upon tightening of the nose member 68 into the recess 66. This providesa fine adjustment to permit the hub 54 and housing member 14 to beseparated sufficiently to eliminate friction therebetween and foradjusting the width of the magnetic gap between the magnet pole piecesand the ends of the axial magnetic core members 48.

As the invention has thus far been described, the speed sensing means 10is adapted to be mounted to the underside of a marine craft or the like(not shown) by means of the bolt 32 and nut 36. The upstanding portion26 of the mounting struc' ture 18 positions the central housing member14 and the hub 54 in a point spaced downwardly from the marine craft andwith the hub 54 facing forwardly and with its axis aligned with thelongitudinal axis of the craft. Thus as the craft moves through thewater the fins 64 act to produce a rotation of the hub 54 at a speedwhich corresponds with the speed at which the craft is moving throughthe water. Rotation of the hub 54 acts through the magnets 62, themagnetic members 48 and 52 and the electromagnetic coil 44 to produce anelectrical current which varies substantially linearly with respect tothe speed of the rotating hub 54 and thus with the speed of the craftthrough the water.

Now referring to FIGS. 4-7 for a more detailed description of the speedindicating means 12 of the present invention a preferred construction istherein illustrated as comprising a substantially box-like housingstructure 80 preferably having an open bottom closed by a plate 72 andadapted to be mounted to a marine craft or the like (not shown) byscrews 74 or the like. The housing structure 80 is intended to carrysome of the components of the electrical system shown diagrammaticallyin FIG. 8 and which will be described in detail below but most of thesehave been eliminated from FIGS. 45 for purposes of clarity.

As can best be seen in FIG. 5, the front face of the housing structure80 is provided with an opening 82 preferably closed by a suitabletransparent material 84 such as glass or the like. An indicator iscarried within the housing structure 80 and is visible through theopening 82 and material 84 and preferably comprises a rearwardly mountedplate 86 having graduated indicia 88 as can best be seen in FIG. 4. Asubstantially arcuate plate 90 mounted to the housing structure 80 in aposition forwardly spaced from the plate 88 and is provided with aplurality of arcuately substantially equally spaced slots 92 which arespaced to coincide with larger lines provided in the indicia 88. As bestbe seen in FIG. 7, the plate 90 is formed with a pair of slots 94 alongits lateral edges and on its inner surface to provide the means forguiding the sliding movement of an arcuate plate 96. t

The plate 96 is disposed within the slots 94 and is therefore positionedintermediate the plates 88 and 90 and is provided with two separate setsof indicia 98 and 100, as can best be seen in FIG. 6, which registerwith the slots 92 depending upon the pivotal position of the plate 96relative to the plate 90. To provide for selective sliding movement ofthe plate 96 an actuating knob 102 is carried on the exterior end of ashaft 104 which is in turn rotatably carried by the housing structure80. The shaft 104 is connected to a perforation 105 provided on one sideof the plate 96 by a linking mechanism 106 so that upon rotation of theshaft 104 in one direction, the plate 96 is moved about a pin (notshown) which is carried by the hous ing 80 and extends through anopening 107 provided in a downwardly extending arm 109 of the plate 96to a position in which the set of indicia 98 is presented through theslots 92, and rotation of the shaft 104 in an opposite direction movesthe plate 96 pivotally to a position in which the set of indicia 100 ispresented through the slots 92.

FIG. 8 illustrates schematically a preferred electrical circuit for thesystem of the present invention which includes the speed indicatingmeans of FIGS. 4-7. The coil 44 is connected by electrical leads 108 toa circuit for a conventional electrical ammeter 110. As previouslydescribed, the coil 44 is carried in the central housing structure 16.The ammeter 110 is preferably carried in the housing structure 80 and isprovided with a pointer 112, as best seen in FIG. 4, which is adapted tomove along the graduated indicia 88. The electrical leads 108 preferablyextend through the mounting structure 18 and the tubular member 30 andconnect to two opposed points on a full wave rectifier bridge generallyindicated at 122 which serves to convert the alternating current outputof the coil to a direct current. A capacitor 120 is preferably connectedacross the other two bridge points to smooth out the pulsating directcurrent output of the bridge. The capacitor 120 is shunted by the seriescombination of the arnmeter 110 and a range selecting and calibrationcircuit consisting of a double throw switching means 124, a pair offixed resistors 126 and 128 and a pair of variable resistors 130 and132.

The switching means 124 is operable to selectively connect the circuitto either one of two resistors 126 and 128. The resistors 126 and 128are of different values so that by actuating the switching means 124 toselect the proper resistor 125 or 128 the particular range of speedindicated by the meter 110 can be selected from two different ranges.The switching means 124 and the resistors 126 and 128 are preferablycarried in the housing structure and the switching means 124 ispreferably connected with the shaft 104 so that rotation of the shaft104 not only provides the proper indicia 98 or visible through theopening 82, but also actuates the switching means 124 to select theproper resistor 126 and 128 for the selected range of indication. Thetrimming resistors 130 and 132 are connected in series with the fixedresistors 126 and 128 respectively to provide for fine adjustment of theresistance of the circuit, and to provide calibration means foradjusting the accuracy of the entire system. I

A knob 134 may if desired be provided on the exterior surface of thehousing structure 80 to provide the means for switching a lighting means136 on and off.

In operation, the speed sensing means 10 is adapted to sense the speedof the marine craft as the craft moves through the water by generatingan electrical current which varies with the speed of the craft. Themeter senses the current produced by the sensing means 10 and actuatesthe pointer 112 to a position corresponding to the particular value ofcurrent produced and the particular resistor 126 or 128 selected. Theparticular set of indicia 98 or 100 which corresponds with theparticular resistor 126 or 128 selected is selected in a visibleposition such that the pointer 112 accurately indicates the speed of thecraft.

The speedometer of FIGS. 1-8 provides a system which may be readilyswitched from a first range of speed indication to a second range ofspeed indication. Thus at low speeds the indicating means 12 can beactuated to provide indicia and response by the pointer for a range ofspeed between 0 and 3 knots for instance. For high speeds the indicatingmeans 12 for example could be actuated to indicate a range of speedbetween 0 and 15 knots. Since no outside power source is necessary thesystem will never be inoperably because of depleted batteries.

Referring now to FIGS. 9-12, there is shown a modification of a speedsensing unit, according to the principle of the invention, provided witha substantially different structure from the one hereinbefore explainedin detail, although capable of operating the speed indicating meansprecedently described as well as a speed indicating means hereinafterdescribed in detail. The speed sensing unit of FIGS. 9-12 comprises ahousing 200 substantially streamlined and adapted for mounting to asubmarine portion of a marine craft, not shown, substantially by as thesame means as previously described relatively to the embodiment of FIGS.1-3. Housing 200 is made of a solid piece of molded material such asbronze or a plastic, and the like and, is provided with a mounting post202 and an indexing pin 204 for adequate mounting upon a mounting plate,not shown, affixed to the marine craft hull. Housing 200 is providedwith two separate longitudinal bores 206 and 208 ion gitudinallyinterconnected by way of a reduced diameter bore 210 and is adapted torotatably support. a hub 212 rearwardly disposed with respect to thenormal direction of flow of the water in which the housing is submergedduring normal operation of the device. Hub 212 is provided with aplurality of inclined impeller blades 214 adapted to rotatably drive hub212 under the action of the water flow. Coaxially disposed so as tosupport hub 212, a shaft member 216 is press fitted in an axial bore 218in the hub, serrations or knurls 220 being provided on a portion of theperiphery of shaft 216 to insure a driving connection between the hub212 and the shaft.

Shaft 216 is adapted to journal with respect to housing 200 by beingsupported therefrom by way of elongated sleeve bushing 222 and shortsleeve 224. Elongated sleeve bushing 222 has an internal bore 226 forfreely accepting shaft 216 therethrough, bore 226 having a reduceddiameter shoulder portion 228 on the rear end thereof, as seen in thedrawing, forming an appropriate bearing surface in which the shaft 216is adapted to journal without play. As hereinafter explained in detail,a coil 258 and magnetic core 243 assembly is disposed in bore 208 inhousing 200 around sleeve bushing 222. The remaining of the space inbore 208, which is closed by a flat end plate 230 through the center ofwhich passes shaft 216, is filled with a potting compound, not shownproviding appropriate electrical insulation and water-proofing of theinterior of the housing such that no special precautions are required toseal water off the inside of the housing. The forward end of shaft 216is supported by way of axial and thrust bearing short bushing 224, bothbushing 224 and sleeve 222 being made preferably of a material such asnylon and being adapted to tightly fit within reduced diameterlongitudinal bore 210 in housing 200.

The forward end of shaft 216 is provided with a threaded portion 232 andis held against longitudinal displacement by means of a nut 234 adaptedto engage such threaded portion 232 of the shaft. Preferably, nut'234has a substantial frictional meshing engagement with the threaded ofthreaded portion 232, or is provided with an appropriate plastic insertsuch that the nut remain locked, for all practical purpose, in anyappropriate position that draws shaft 216 inwardly intothe housing untilthe end 236 thereof just engages the end surface 238 of a shoulderedplug 240 fitted in a reduced diameter bore portion 242 of bore 206. Plug240 is also made preferably of a material such as nylon and if sodesired, it may alternately consist of a threaded member engaging athreaded portion of bore 242 so as to be capable of providinglongitudinal adjustment of the abutting surface 238 engaged by theforward end of shaft 216.

Longitudinally disposed in bore 208 there is a cup-like hollow magneticcore member 244, best seen in perspective schematic view in FIG. 11,provided with projecting pole pieces 246 and 248, within which isdisposed a tubular magnetic core member 250 provided with projectingpole pieces 252 and 254. Cup-like magnetic core member 244 has aninwardly radially extending end flange portion 256 engaging the end oftubular member 250, and cup-like member 244 and tubular member 250,which are both made of a magnetic permeable material, together definethe magnetic core, generally designated at 243, for a coil winding 258wound around tubular member 250 in the space separating the outersurface of tubular member 250 with the inner surface of cup-like member244. As illustrated at FIG. 11, the pair of pole pieces 246 and 248 ofthe hollow magnetic core member 244 are disposed on an imaginarydiameter which is orthogonal to the imaginary diameter on which aredisposed the pole pieces 252 and 254 of the inner tubular core member250. Coil 258 is provided with a pair of leads 260 for electricalconnection to an appropriate speed indicating means, which may be of thetype hereinbefore described and shown at FIGS. 48 or, alternately, ofthe type to be hereinafter explained in detail.

The flat forward end face 261 of hub 212 is provided with a plurality oflongitudinally elongated disposed cavities 262 concentrically andsymetrically disposed about shaft 216. In each longitudinally disposedcavity 262 there is a permanent rod magnet 264, four of which are shownin FIG. 12. The permanent magnets 264 are alternately disposed withrespect to magnetic polarity so as to present pole pieces of alternatepolarity in opposition to the pole pieces 246, 248, 250, and 254 ofmagnetic core 243 of coil 258 during rotation of hub 212.

It can thus be seen that when hub 212 is rotated by inclined impellerblades 214 while the craft is moving in the water, a rotating magneticfield created by rotating magnets 264 contained in the hub is caused toinduce into stationary coil 258 an alternating current of a frequencylinearly dependent upon the speed of revolution of the hub.

FIGS. 13-14 depict an alternate construction of the magnet arrangementin hub 212, wherein the magnet consists of a substantially cylindrical,or frusto-conical, sleeve magnet 266 adapted to be imbedded in thematerial of hub 212 around shaft 216 and concentrically therewith,sleeve 266 being provided on its end proximate housing 200 withtooth-like projecting pole pieces 268 of alternate magnetic polarities.

The magnetic gap between the pole pieces of the coil core 243 and thepole pieces of magnets 264 or 266 in hub 212 which detennines thevoltage of the current induced in coil 258, such magnetic gap beingindicated at 270 in FIG. 9, is precisely determined at the factoryduring assembly of the sensing unit, and remains consistent over aprolonged period of use. In order to reestablish the original gap, it issufficient to rotate nut 234 in a direction that advances shaft 216towards the left, as seen in the drawing, until its end 236 just engagesthe end surface 238 of plug 240. This adjustment is accomplished byintroducing an appropriate tool through an access aperture, not shown,leading into bore 206 of housing 200, and by replacing, by cementing forexample, the cover normally obturating such access aperture beforereturning the craft to the water after routine drydock inspection andmaintainance of the hull.

It can be seen that the configuration of FIG. 9-14 provides forsubstantial protection of the rotating hub and impeller blades againstdamage as a result of collision with submerged objects in view of thefact that the forward portion of housing 200 acts as a leading edge andprotector for the hub, rearwardly positioned with respect to the normaldirection of motion of the craft. It can also be seen that in view ofthe streamlined shape of the housing there is a considerable reductionin the possibility of weeds and other stringy material becomingentangled with the impeller blades and interfering with or preventingthe rotation of the hub. There is also very little possibility of dirtbeing introduced between the opposed adjoining surfaces of the housingand the hub at the gap 270, and any dirt which may tend to penetratetherebetween is thrown out as a result of the centrifugal forcedeveloped by hub 212 when rotating or by the rolling action between thestationary surface of the housing end and the rotating end surface ofthe hub.

Referring now to FIGS. 15-46, there is shown respectively an electricalcircuit, including an electrical meter, and an appropriate electricalmeter dial for use with the speed sensing unit of FIGS. 914 as well asthe speed sensing unit of FIGS. 1-3. As shown in FIG. 15, the coil 258of the speed sensing unit is connected by means of leads 260 across adiagonal of a full-wave rectifier bridge 272 comprising diodes 274. Anammeter 276 is connected across the other diagonal of the rectifierbridge so as to provide an indication of the current rectified by thebridge which is substantially proportional to the frequency of thecurrent generated by coil 258, i.e., substantially proportional to thespeed of the craft. A capacitor 278 is also connected across the outputof bridge 272 for the purpose of smoothing out the pulsing directcurrent. An variable resistor 280 is connected in shunt across the metersuch that only a portion of the rectified current passes through themeter and such that, by appropriate adjustment of the variable resistor,the meter may be appropriately calibrated to give an accurate indicationof the speed at which the craft is moving with respect to the water.

As shown in FIG. 16, ammeter 276 is provided with a dial preferablycalibrated in appropriate speed indication units, such as knots, and haspreferably a non-linear scale comprising graduations 278 correspondingto speed indicating indicia 280. The meter pointer 282 is displaceableto the appropriate graduation indicating the speed of the craft, thegraduated scale being such that a much greater distance separateconsecutive graduations indicating substantially low speed as comparedto the distance separating consecutive graduations indicatingsubstantially high speed. Such a non-linear scale presents particularadvantage for relatively slow marine craft such as sailing vessels wherean accurate speed indicator for low speed is of great importance forprecise navigation and in view of the normally relatively low speed ofthe craft under normal wind conditions.

Th e circuit of FIG. 15 is particularly designed to provide non-lineardisplacement of the pointer so as to provide an expanded scale givinggreater displacement for one unit of speed at the low range of theinstrument and shorter displacement of the pointer at the high range ofthe instrument. The circuit of FIG. include diodes 274 preferably of theIN34A type or equivalent thereof, forming the rectifying bridge 272, acalibration variable resistor of 10 kohm, an ammeter 276 providing fullscale deviation for 1 milliampere and a shunt capacitor 278 of 100microfarad. The capacitor 278 acts partly as a bypass path for theunidirectional current pulses at the output of rectifier bridge 272having relatively high frequency pulses when the craft is moving atsubstantially high speed, thereby allowing a relatively smaller portionof the total current to pass through the meter for high frequency pulsedcurrents detected by the bridge circuit, while allowing a greaterproportion of the total current to pass through the meter for relativelylow frequency pulsed currents detected by the circuit and correspondingto, relatively low speed of the craft.

Having thus described the invention by way of examples of typicalstructural embodiments thereof, changes and modifications whereof willbe readily apparent to those skilled in the art, what is sought to beprotected by United States Letters Patent is as follows:

1. A speedometer for marine craft and the like comprising:

a streamlined housing for mounting on said craft, said housing beingnormally submerged in water and having a fiat end plate;

a streamlined hub supported from said housing and having an end faceproximate the end plate of said housing, said hub being freely rotatablerelatively to said housing;

impeller means dependent from said hub for rotating said hub when saidcraft moves relatively to said water;

permanent magnets mounted in said hub proximate the end face thereof andabout the axis of rotation of said hub with an end of each of saidmagnets proximate the flat end plate of said housing, said permanentmagnets being defined by a hollow cylindrical member having at least apair of pole pieces of alternate magnetic polarities oriented so as toform axially extending magnetic fields;

an electrical coil in said housing;

magnetically permeable core members in said housing each having an endproximate the flat end plate thereof axially spaced a short distancefrom the ends of said magnets in the hub to form a magnetic gaptherewith and another end arranged to form a magnetic path to said coil;

speed indicatingmeans comprising an electrical meter connected to saidcoil for measuring the current induced in said coil as a function of thespeed of rotation of said magnets mounted in said hub, said meter havinga dial graduated in speed indicating indicia;

a current rectifying circuit having an input connected across said coiland an output connected across said meter; and adjustable scaleexpanding means dependent from said circuit for enabling said meter toprovide speed indications at a larger scale for low speed of said craftthan for high speed of said craft 2. The speedometer of claim 1 furthercomprising:

at least two current limiting resistors of different values,

switch means for electrically connecting one of said resistors at a timein series between said meter and said current rectifying circuit so asto provide a variety of speed indicating ranges for said meter, and

a shunt capacitor connected across the output of said rectifying circuitfor reducing the ripple of the current at said output.

3. The speedometer of claim 2 further comprising:

a variable resistor in series with each of said current limitingresistors for fine calibration of the speed indicating range of themeter corresponding to each of said current limiting resistors.

4. The speedometer of claim 3 further comprising:

a scale of speed indicia for each speed indicating range of said meter,and

means dependent from said switch means and operatively connected to eachsaid scale of speed indicia for displaying the scale of speed indiciacorresponding to the speed indicating range of said meter resulting froma predetermined resistor being switched in series between said meter andsaid current rectifying circuit.

5. The speedometer of claim 1 further comprising:

an adjustable shunt resistor electrically connected across the meter forfine calibration of the speed indicating range of said meter.

6. The speedometer of claim 5 further comprising:

a shunt capacitor electrically connected across the output of thecurrent rectifying circuit for bypassing a greater proportion of thetotal pulsed current at such output at high frequency than at lowfrequency, and

a non-linear speed indicating scale dial on said meter provided with anexpanded low speed scale.

7. The speedometer of claim 1 wherein said magnetically permeable coremembers comprise:

a pair of longitudinally disposed parallel magnetically permeablemembers each having an end proximate the flat end plate of said housing;and

a transversely disposed magnetically permeable member in abuttingjuxtaposition with the other end of each of said longitudinally disposedmember, said transversely disposed member having said coil woundtherearound.

8. The speedometer of claim 1 wherein said hub is longitudinallyadjustably positionable with respect to said housing for defining apredetermined axial magnetic gap between the ends of said magnets insaid hub and the ends of said magnetically permeable core members insaid housing.

9. A speedometer for marine craft and the like comprising:

a streamlined housing for mounting on said craft, said housing beingnormally submerged in water and having a flat end plate;

a streamlined hub supported from said housing and having an end faceproximate the end plate of said housing, said hub being freely rotatablerelatively to said housing;

impeller means dependent from said hub for rotating said hub when saidcraft moves relatively to said water;

permanent magnets mounted in said hub proximate the end face thereof andabout the axis of rotation of said hub with an end of each of saidmagnets proximate the flat end plate of said housing, said permanentmagnets being oriented so as to form axially extending magnetic fields;an electrical coil in said housing;

magnetically permeable core members in said hosing each having an endproximate the flat end plate thereof axially spaced a short distancefrom the ends of said magnets in the hub to form a magnetic gaptherewith and another end arranged to form a magnetic path to said coil;

speed indicating means comprising an electrical meter connected to saidcoil for measuring the current induced in said coil as a function of thespeed of rotation of said magnets mounted in said hub, said meter havinga dial graduated in speed indicating indicia;

a current rectifying circuit having an input connected across said coiland an output connected across said meter; and

adjustable scale expanding means dependent from said circuit forenabling said meter to provide speed indications at a larger scale forlow speed of said craft than for high speed of said craft;

wherein said magnetically permeable core members comprise:

a pair of coaxially disposed inner and outer tubular magneticallypermeable members each having a first end proximate the flat end plateof said housing, said electrical coil being wound on the periphery ofsaid inner member;

a radially extending flange portion dependent from one of said tubularmember at a second end thereof remote from the end plate of said housingand arranged in abutting engagement with the other of said tubularmember; and

at least a pair of diametrically opposed tooth-like projecting polepieces formed on the first end of said tubular members, the pair of polepieces on the end of the inner tubular member being on a diametersubstantially orthogonal to the diameter on which are disposed the polepieces of the outer tubular member.

10. The speedometer of claim 8 wherein said hub is longitudinallyadjustably positionable with respect to said housing for defining apredetermined axial magnetic gap between the ends of said magnets insaid hub and the ends of said magnetically permeable core members insaid housing.

1 1. The speedometer of claim 8 further comprising:

at least two current limiting resistors of different values,

switch means for electrically connecting one of said resistors at a timein series between said meter and said current rectifying circuit so asto provide a variety of speed indicating ranges for said meter, and

a shunt capacitor connected across the output of said rectifying circuitfor reducing the ripple of the current at said output.

12. The speedometer of claim 1 1 further comprising:

a variable resistor in series with each of said current limitingresistors for fine calibration of the speed indicating range of themeter corresponding to each of said current limiting resistors.

13. The speedometer of claim 12 further comprising:

a scale of speed indicia for each speed indicating range of said meter,and

means dependent from said switch means and operatively connected to eachsaid scale of speed indicia for displaying the scale of speed indiciacorresponding to the speed indicating range of said meter resulting froma predetermined resistor being switched in series between said meter andsaid rectifying circuit.

14. The speedometer of claim 8 further comprising:

an adjustable shunt resistor electrically connected across the meter forfine calibration of the speed indicating range of said meter.

15. The speedometer of claim 8 further comprising:

a shunt capacitor electrically connected across the output of thecurrent rectifying circuit for bypassing a greater proportion of thetotal pulsed current at such output at high frequency than at lowfrequency, and

a non-linear speed indicating scale dial on said meter provided with anexpanded low speed scale.

16. The speedometer of claim 8 wherein said permanent magnets in saidhub are at least a pair of rod magnets disposed symmetrically about theaxis of rotation of said hub.

17. The speedometer of claim 8 wherein said permanent magnets in saidhub are defined by a hollow cylindrical member having at least a pair ofpole pieces of alternate magnetic polarities.

UNITED STATES PATENT OFFICE" CERTIFICATE OF CORRECTION Patent No.3,657,924 Dated April 25, 1972 Inventor(s) William H. Kirk It ,iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below: 0

IN THE SPECIFICATION Column 4, line 24, change "38" to 28 Column 6, line9, change "125" to 126 IN THE CLAIMS Column 10, line 56, change "hosing"to housing Signed and sealed this 29th day of August 1972.

(SEAL) Attest:

EDWARD M.'FIETCHER,' JR. ROBERT GOTTSGHALK Arresting OfficerCommissioner of Patents USCOMM-DC 603764 69 FORM P0-1050 (10-69) a u.s.covznunsm PRINTING OFFICE 19! 0-3664

1. A speedometer for marine craft and the like comprising: a streamlinedhousing for mounting on said craft, said housing being normallysubmerged in water and having a flat end plate; a streamlined hubsupported from said housing and having an end face proximate the endplate of said housing, said hub being freely rotatable relatively tosaid housing; impeller means dependent from said hub for rotating saidhub when said craft moves relatively to said water; permanent magnetsmounted in said hub proximate the end face thereof and about the axis ofrotation of said hub with an end of each of said magnets proximate theflat end plate of said housing, said permanent magnets being defined bya hollow cylindrical member having at least a pair of pole pieces ofalternate magnetic polarities oriented so as to form axially extendingmagnetic fields; an electrical coil in said housing; magneticallypermeable core members in said housing each having an end proximate theflat end plate thereof axially spaced a short distance from the ends ofsaid magnets in the hub to form a magnetic gap therewith and another endarranged to form a magnetic path to said coil; speed indicating meanscomprising an electrical meter connected to said coil for measuring thecurrent induced in said coil as a function of the speed of rotation ofsaid magnets mounted in said hub, said meter having a dial graduated inspeed indicating indicia; a current rectifying circuit having an inputconnected across said coil and an output connected across said meter;and adjustable scale expanding means dependent from said circuit forenabling said meter to provide speed indications at a larger scale forlow speed of said craft than for high speed of said craft
 2. Thespeedometer of claim 1 further comprising: at least two current limitingresistors of different values, switch means for electrically connectingone of said resistors at a time in series between said meter and saidcurrent rectifying circuit so as to provide a variety of speedindicating ranges for said meter, and a shunt capacitor connected acrossthe output of said rectifying circuit for reducing the ripple of thecurrent at said output.
 3. The speedometer of claim 2 furthercomprising: a variable resistor in series with each of said currentlimiting resistors for fine calibration of the speed indicating range ofthe meter corresponding to each of said current limiting resistors. 4.The speedometer of claim 3 further comprising: a scale of speed indiciafor each speed indicating range of said meter, and means dependent fromsaid switch means and operatively connected to each said scale of speedindicia for displaying the scale of speed indicia corresponding to thespeed indicating range of said meter resulting from a predeterminedresistor being switched in series between said meter and said currentrectifying circuit.
 5. The speedometer of claim 1 further comprising: anadjustable shunt resistor electrically connected across the meter forfine calibration of the speed indicating range of said meter.
 6. Thespeedometer of claim 5 further comprising: a shunt capacitorelectrically connected across the output of the current rectifyingcircuit for bypassing a greater proportion of the total pulsed currentat such output at high frequency than at low frequency, and a non-linearspeed indicating scale dial on said meter provided with an expanded lowspeed scale.
 7. The speedometer of claim 1 wherein said magneticallypermeable core members comprise: a pair of longitudinally disposedparallel magnetically permeable members each having an end proximate theflat end plate of said housing; and a transversely disposed magneticallypermeable member in abutting juxtaposition with the other end of each ofsaid longitudinally disposed member, said transversely disposed memberhaving said coil wound therearound.
 8. The speedometer of claim 1wherein said hub is longitudinally adjustably positionable with respectto said housing for defining a predetermined axial magnetic gap betweenthe ends of said magnets in said hub and the ends of said magneticallypermeable core members in said housing.
 9. A speedometer for marinecraft and the like comprising: a streamlined housing for mounting onsaid craft, said housing being normally submerged in water and having aflat end plate; a streamlined hub supported from said housing and havingan end face proximate the end plate of said housing, said hub beingfreely rotatable relatively to said housing; impeller means dependentfrom said hub for rotating said hub when said craft moves relatively tosaid water; permanent magnets mounted in said hub proximate the end facethereof and about the axis of rotation of said hub with an end of eachof said magnets proximate the flat end plate of said housing, saidpermanent magnets being oriented so as to form axially extendingmagnetic fields; an electrical coil in said housing; magneticallypermeable core members in said hosing each having an end proximate theflat end plate thereof axially spaced a short distance from the ends ofsaid magnets in the hub to form a magnetic gap therewith and another endarranged to form a magnetic path to said coil; speed indicating meanscomprising an electrical meter connected to said coil for measuring thecurrent induced in said coil as a function of the speed of rotation ofsaid magnets mounted in said hub, said meter having a dial graduated inspeed indicating indicia; a current rectifying circuit having an inputconnected across said coil and an output connected across said meter;and adjustable scale expanding means dependent from said circuit forenabling said meter to provide speed indications at a larger scale forlow speed of said craft than for high speed of said craft; wherein saidmagnetically permeable core members comprise: a pair of coaxiallydisposed inner and outer tubular magnetically permeable members eachhaving a first end proximate the flat end plate of said housing, saidelectrical coil being wound on the periphery of said inner member; aradially extending flange portion dependent from one of said tubularmember at a second end thereof remote from the end plate of said housingand arranged in abutting engagement with the other of said tubularmember; and at least a pair of diametrically opposed tooth-likeprojecting pole pieces formed on the first end of said tubular members,the pair of pole pieces on the end of the inner tubular member being ona diameter substantially orthogonal to the diameter on which aredisposed the pole pieces of the outer tubular member.
 10. Thespeedometer of claim 8 wherein said hub is longitudinally adjustablypositionable with respect to said housing for defining a predeterminedaxial magnetic gap between the ends of said magnets in said hub and theends of said magnetically permeable core members in said housing. 11.The speedometer of claim 8 further comprising: at least two currentlimiting resistors of different values, switch means for electricallyconnecting one of said resistors at a time in series between said meterand said current rectifying circuit so as to provide a variety of speedindicating ranges for said meter, and a shunt capacitor connected acrossthe output of said rectifying circuit for reducing the ripple of thecurrent at said output.
 12. The speedometer of claim 11 furthercomprising: a variable resistor in series with each of said currentlimiting resistors for fine calibration of the speed indicating range ofthe meter corresponding to each of said current limiting resistors. 13.The speedometer of claim 12 further comprising: a scale of speed indiciafor each speed iNdicating range of said meter, and means dependent fromsaid switch means and operatively connected to each said scale of speedindicia for displaying the scale of speed indicia corresponding to thespeed indicating range of said meter resulting from a predeterminedresistor being switched in series between said meter and said rectifyingcircuit.
 14. The speedometer of claim 8 further comprising: anadjustable shunt resistor electrically connected across the meter forfine calibration of the speed indicating range of said meter.
 15. Thespeedometer of claim 8 further comprising: a shunt capacitorelectrically connected across the output of the current rectifyingcircuit for bypassing a greater proportion of the total pulsed currentat such output at high frequency than at low frequency, and a non-linearspeed indicating scale dial on said meter provided with an expanded lowspeed scale.
 16. The speedometer of claim 8 wherein said permanentmagnets in said hub are at least a pair of rod magnets disposedsymmetrically about the axis of rotation of said hub.
 17. Thespeedometer of claim 8 wherein said permanent magnets in said hub aredefined by a hollow cylindrical member having at least a pair of polepieces of alternate magnetic polarities.